1. Field of the Invention
The present invention relates to a liquid agent for treating contaminated soil, a method for producing the same, and a method for treating soil using the same.
2. Related Background Art
A large amount of chemical compounds or chemical products have been produced with the recent rapid progress in technology and science. Since most of these compounds or products did not originally exist in nature, they are hardly decomposed naturally and thus, accumulate in the natural environment resulting in environmental pollution. In particular, land where many people live is readily affected by artificial pollution. Since water circulates through land, atmosphere and hydrosphere, the environmental pollution in land will spread globally. Well-known examples of pollutants in soil or land include organic compounds such as gasoline, organochloric chemicals such as PCB, teratogenic agrichemicals such as dioxin, as well as radioactive compounds. Fuel such as gasoline is commonly stocked in a huge amount in the underground tanks of gas stations etc. Thus, fuel leak from deteriorated or broken tanks into soil is now a serious social problem. Further, organochloric chemicals, e.g. chlorinated aliphatic hydrocarbons such as trichloroethylene and tetrachloroethylene, were once extensively used for cleaning fine parts as well as for dry cleaning, and large scale pollution of soil and ground water due to the leakage of these chemicals has been gradually revealed. Since such organochloric chemicals are teratogenic and carcinogenic to adversely affect the biological world, purification of the polluted soil or ground water is now an issue to be solved immediately in addition to the isolation of the pollution source.
Methods for remedying soil polluted with these pollutants include, for example, heat treatment of the dug-up soil, vacuum extraction of the contaminant from the polluted soil, and microbial degradation of the pollutant in soil. Although the heat treatment can almost completely remedy the soil, the soil must be dug up so that soil under structures cannot be purified. Moreover, it is unsuitable for large-scale treatment because of the immense costs of digging and heating. Although the vacuum extraction method is a simple and economical purification method, organochloric compounds in a concentration of several ppm or lower cannot be efficiently removed and this remediation process requires time in annual scale. On the other hand, microbial purification does not require dig-up of soil, so it can purify the soil under structures, and use of microorganisms of high degradation activity enables short-time purification. Thus, this economical and effective purification method has been attracting attention lately.
U.S. Pat. No. 5,133,625 discloses a method for efficiently purifying soil using an extensible injection pipe through which the injection pressure, flow rate, and temperature can be determined to control the injection pressure, thus to control the concentrations of microbes and nutrients in the soil. U.S. Pat. Nos. 4,442,895 and 5,032,042 disclose a method of effective in situ microbial remediation of polluted soil, where cracks are formed in the soil using a liquid or a gas injected into the soil with pressure from an injection well. U.S. Pat. No. 5,111,883 discloses a method for injecting chemicals vertically or horizontally into a limited region of the soil by setting the relative position of the injection and extraction wells.
Injection of a pollutant-decomposing microorganism, nutrients, an inducer, oxygen, and other chemicals into the soil is considered to be essential for the microbial remediation of polluted soil. However, according to the conventional injection methods, an extremely large amount should be injected to remedy a wide area, since the liquid agent is injected from the injection element to fill the soil pore space. Such a process increases the processing period, labor and material costs, resulting in increased remediation expenses. Differing from chemicals, microorganisms can spontaneously grow and multiply when certain growth conditions such as nutrient are satisfied. If a liquid agent containing the microorganism and nutrient can be injected in an amount as small as possible into a wide area of soil and the microorganism can grow in the soil to decompose pollutants, the purification expenses is considerably decreased. However, when the necessary amount of the microorganism and nutrient is injected into a wide area after dilution, the processing period and labor required for injection do not decrease. Further, such a method that the liquid agent will fill most of the soil pore space may cause soil fluidization and soften the ground with a high possibility, it cannot be applied to the soil under heavy structures. Moreover, the liquid agent injected into the soil penetrates into the deeper layers and diffuses into underground streams. Therefore, mobile microorganisms and nutrients will not remain within the desired area and are lost. Thus, reinjection is required, making it difficult to remedy soil at a low cost. Further, the runoff of the microorganisms and nutrients may cause secondary environmental pollution. Consequently, in microbial soil purification, a method for injecting using a small amount of the agent into a wide area of soil is required without filling all the pore space of the soil.